1. Field of the Invention
The present invention relates to a thermosetting resin composition. More particularly, the present invention relates to a thermosetting resin composition comprising a modified aromatic imide oligomer having terminal hydroxyl groups and an organic compound having at least one epoxy group.
The thermosetting resin composition of the present invention is useful as a thermosetting imide-epoxy type adhesive agent and molding material having an excellent heat resistance.
2. Description of the Related Arts
Generally, although epoxy resin compositions and cured articles thereof exhibit an excellent dimensional stability and electric properties, and thus are useful in various technical fields, the cured articles of the epoxy resin composition do not always have a satisfactory heat resistance.
Therefore, in an attempt to improve the heat resistance of the epoxy resin compositions, an organic compound having epoxy groups is used in combination with a polyimide or imide oligomer compound exhibiting a high heat resistance. In general, however the polyimide and imide oligomer compounds exhibit a very poor solubility in organic solvents, and an extremely high softening point, and thus cannot be easily and uniformly mixed with the organic compound having epoxy groups, and therefore, it is difficult to prepare a uniform resinous composition of the organic compound having epoxy groups with the polyimide or imide oligomer compound.
To overcome the above-mentioned difficulty, attempts have been made to mix a polyamic acid, which is a precursor of the polyimide and exhibits an excellent solubility in various organic solvents, with the organic compound having epoxy groups. The polyamic acid is disadvantageous, however, in that the conversion of the polyamic acid to the corresponding polyimide at a high temperature causes a generation of a by-product consisting of water, and the generated water causes a deterioration in the physical properties of the resultant cured polyimide article.
In a recent attempt to overcome the above-mentioned disadvantages, the organic compound having epoxy groups was used in combination with an imide oligomer having a low molecular weight and provided with terminal groups reactive to the epoxy groups, to provide a thermosetting resin composition. For example, Japanese Unexamined Patent Publication (Kokai) No. 54-64597 discloses a modified imide oligomer having terminal hydroxyl groups, which is assumed to be prepared by using 5-bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride; U.S. Pat. No. 4,820,779 discloses a carbinol structure-containing polyimide oligomer produced from carbinoltetracarboxylic acid, an aromatic diamine, and a primary amine or dicarboxylic acid, and having terminal groups reactive to the epoxy groups, for example, terminal amine, phenol, thiol or carboxyl groups; U.S. Pat. No. 4,757,150 discloses an ether imide oligomer having terminal hydroxyl groups, prepared from bisphenol A tetracarboxylic dianhydride; and Japanese Unexamined Patent Publication (Kokai) No. 63-75034 discloses a thermosetting modified imide oligomer having an aromatic imide structure formed by an imide-forming reaction of an m,m'-type aromatic diamine compound with a tetracarboxylic dianhydride compound and terminal addition-reactive groups, for example, maleic anhydride residue.
The above-mentioned conventional imide oligomers having terminal hydroxyl groups do not always have a satisfactory heat resistance, and further, must be prepared by using very special and expensive tetracarboxylic acid compounds, and accordingly, are difficult to prepare or obtain, and thus to be industrially utilized.
As described in Comparative Example 1 of U.S. Pat. No. 4,820,779, a modified imide oligomer having a terminal hydroxyl group and prepared by using benzophenone tetracarboxylic dianhydride, which is popular as an aromatic tetracarboxylic and component, is substantially insoluble in organic solvents, and thus is useless as a component of epoxy resin composition.